Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$87.82	5.380%	$92.5447	$92.54	$92.55	$92.50
Purchase #2	$32.87	5.527%	$34.6867	$34.69	$34.70	$34.70
Purchase #3	$152.34	13.182%	$172.4215	$172.42	$172.40	$172.40
Purchase #4	$19.27	12.457%	$21.6705	$21.67	$21.65	$21.70
Purchase #5	$137.69	10.568%	$152.2411	$152.24	$152.25	$152.20
Purchase #6	$137.69	5.402%	$145.128	$145.13	$145.15	$145.10
Purchase #7	$152.50	12.609%	$171.7287	$171.73	$171.75	$171.70
7 purchase totals =	$720.18		$790.4212	$790.42	$790.45	$790.30